How to deal with the inconsistency of lithium-ion batteries

The inconsistency of battery core performance is formed during processing and deepened during use. The battery cells in the same battery pack are always weak for the weak, and become weaker at an accelerated rate. The degree of dispersion of the parameters between the single cells increases as the degree of aging deepens. At present, engineers must consider three aspects to deal with the inconsistency of single cells. Single battery sorting, thermal management after grouping, the battery management system provides equalization function when there is a small amount of inconsistency. 3.1 Separate batteries of different batches and theoretically do not put them together for use. Even batteries of the same batch must be screened, and batteries with relatively concentrated parameters are placed in a battery pack and in the same battery pack. The purpose of sorting is to select cells with similar parameters. The sorting method has been studied for many years, and it is mainly divided into two categories: static sorting and dynamic sorting. Static sorting is to screen for the characteristic parameters such as open circuit voltage, internal resistance and capacity of the cells, select the target parameters, introduce statistical algorithms, set the screening criteria, and finally divide the cells of the same batch into several groups. Dynamic screening is based on the characteristics of the battery cell during the charging and discharging process. Some choose the constant current and constant voltage charging process, some choose the pulse shock charging and discharging process, and some compare their own charging and discharging curves. relationship. Combining dynamic and static sorting, static screening is used for preliminary grouping, and dynamic screening is performed on this basis, so that more groups can be divided and screening accuracy is higher, but the cost will rise accordingly. Here is a small reflection of the importance of the processing scale of a handful of power lithium-ion batteries. Large-scale shipments allow manufacturers to perform finer sorting and obtain battery packs with closer performance. If the output is too small and there are too many groups, no one batch can be equipped with a battery pack, no matter how good the method is. 3.2 Thermal management aims at the battery cells with inconsistent internal resistance and the problem of different heat. The addition of the thermal management system can adjust the temperature difference of the entire battery pack to keep it within a small range. Cells that generate more heat still have a high temperature rise, but they will not be far apart from other cells, and there will be no significant difference in degradation level. 3.3 Balance the inconsistency of the battery cells. The terminal voltage of some cells always leads other cells and reaches the control threshold first, resulting in the reduction of the capacity of the entire system. In order to solve this problem, the battery management system BMS has designed a balancing function. A certain battery cell is the first to reach the charge cut-off voltage, while the voltage of the other cells is obviously lagging behind. The BMS activates the charge equalization function, or connects a resistor to discharge part of the high-voltage battery's power, or transfer the energy away and put it to a low level. The voltage cell goes up. In this way, the charging cut-off condition is lifted, the charging process is restarted, and the battery pack is charged with more power. Until now, the inconsistency of batteries is still an important area of u200bu200bresearch in the industry. No matter how high the energy density of the battery cell is, and the inconsistency will disrupt the situation, the capacity of the battery pack will be greatly reduced. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: Why does lithium-ion battery wear out? How to fix it